package com.iverson.java8;

import org.junit.Test;

import java.io.PrintStream;
import java.util.Comparator;
import java.util.function.BiFunction;
import java.util.function.BiPredicate;
import java.util.function.Consumer;
import java.util.function.Function;

/**
 * @program: lambda
 * @author: ouguoxin
 * @create: 2020-11-13 18:22
 **/
/*
 * 一、方法引用：若 Lambda 体中的功能，已经有方法提供了实现，可以使用方法引用
 * 			  （可以将方法引用理解为 Lambda 表达式的另外一种表现形式）
 *
 * 1. 对象的引用 :: 实例方法名
 *
 * 2. 类名 :: 静态方法名
 *
 * 3. 类名 :: 实例方法名
 *
 * 注意：
 * 	 ① 数列表和返回值类型保持一致！
 * 	 ②若Lambda 的参数列表的第一个参数，是实例方法的调用者，第二个参数(或无参)是实例方法的参数时，格式： ClassName::MethodName
 *
 * 二、构造器引用 :构造器的参数列表，需要与函数式接口中参数列表保持一致！
 *
 * 1. 类名 :: new
 *
 * 三、数组引用
 *
 * 	类型[] :: new;
 *
 *
 */

public class TestMethodRef {

    @Test
    public void test1() {
        PrintStream ps = System.out;
        Consumer<String> con = (str) -> ps.println(str);

        System.out.println("----------------");

        Consumer<String> con2 = ps::println;
        con2.accept("Hello java8!");

        Consumer<String> con3 = System.out::println;
    }

    //类名::静态方法名

    @Test
    public void test3() {
        BiFunction<Double,Double,Double> function = (x,y) -> Math.max(x,y);
        System.out.println(function.apply(1.5,22.2));

        System.out.println("------------------");

        BiFunction<Double,Double,Double> function1 = Math::max;
        System.out.println(function1.apply(1.2,1.5));
    }

    @Test
    public void test4() {
        Comparator<Integer> com = (x,y) -> Integer.compare(x,y);

        System.out.println("--------------------");

        Comparator<Integer> com2 = Integer::compare;
        int com3 = com2.compare(1,1);
        System.out.println(com3);
    }

    //类名::实例方法名
    @Test
    public void test5() {
        BiPredicate<String,String> bp = (x,y)->x.equals(y);
        System.out.println(bp.test("abcde","abcde"));

        System.out.println("-----------");

        BiPredicate<String,String> bp2 = String::equals;
        System.out.println(bp2.test("abc","abc"));

        System.out.println("-------------");

        Function<Employee,String> fun = (employee -> employee.show());
        System.out.println(fun.apply(new Employee()));

        System.out.println("---------------");

        Function<Employee,String> fun2 = Employee::show;
        System.out.println(fun2.apply(new Employee()));
    }

    //构造器引用
    @Test
    public void test7() {
        Function<String,Employee> fun = Employee::new;

        BiFunction<String, Integer , Employee> fun2 = Employee::new;
        Employee e = fun.apply("qqq");
        System.out.println(e.toString());
    }

    @Test
    public void test8() {
        Function<Integer,String[]> fun = (args) -> new String[args];
        String[] strs = fun.apply(10);
        System.out.println(strs.length);

        System.out.println("------------");
        Function<Integer,Employee[]> fun2 = Employee[] :: new;
        Employee[] employees = fun2.apply(20);
        System.out.println(employees.length);
    }

}

